The present invention relates to hydraulic or pneumatic seals. Small lightweight efficient hydraulic components are needed in many applications in the aerospace industry. These components require long lasting, reliable, easy to assemble high pressure seals which take up a minimum of space within the component. In prior art seals to prevent leakage between a cylindrical sleeve and a surrounding valve body an elastomeric O-ring is normally located in a circumferential groove in the sleeve with a backup ring located on one or both sides of the elastomeric O-ring. These wear-resistant backup rings are made with material having a low coefficient of friction such as polytetrafluoroethylene (Teflon). Some rings are pure Teflon and other rings are made of Teflon filled material. They protect the O-ring and prevent it from being extruded into the annular gap between the sleeve and the valve body when high pressure is placed on the seal.
The backup rings, sometimes termed as antiextrusion devices may have cross-sectional shapes in the form of triangles (U.S. Pat. No. 3,455,566). Prior patents also disclose rectangular cross-sectional shapes as well as rectangles with one curved side facing toward or away from the elastomeric O-ring (U.S. Pat. No. 2,456,356). Backup rings are also found with cross sections in the form of a truncated rectangle which mates with the sloped side of the groove (U.S. Pat. No. 2,462,586). The backup rings may be endless or continuous (uncut) in which case they may be difficult to emplace in a groove on the sleeve without distorting the ring beyond its elastic limits.
For ease of installation on the valve sleeve the backup ring may be scarf cut (U.S. Pat. No. 2,462,586) to permit it to pass over intervening lands on the sleeve. The backup ring may also be made in expandable helical form with more than one circumferential loop (U.S. Pat. No. 2,749,193). The cross-sectional shape of these helical loop backup rings when emplaced in the groove is usually in the form of a square or rectangle adjacent the O-ring.
The cross section of the circumferential groove in the sleeve has usually been rectangular, (U.S. Pat. No. 2,456,356), however, some patents (U.S. Pat. Nos. 2,437,814 and 2,462,586) disclosed grooves with trapezoidal cross sections with the longer base opening outward. In another patent the trapezoidal groove had the longer base toward the inside of the groove (U.S. Pat. No. 2,427,787).
The O-ring is usually in the shape of a torus (U.S. Pat. Nos. 2,456,356 and 2,747,954) with a circular cross section, however, some sealing rings have a T-shape (U.S. Pat. No. 2,349,170) or an elliptical shape (U.S. Pat. No. 3,455,566) cross section.
Some of the failures of the prior art seals have been attributed to the short life of O-rings. This short operating life is in part due to damage caused during installation to the backup rings which protect the O-ring. This damage is a result of the stretching or deformation of the backup rings beyond their elastic limits in the process of installing them over the lands on the sleeve in order to install them in the groove. When the backup ring breaks down it permits the O-ring to be extruded into the annular space between the sleeve and the surrounding valve body. The elastomeric O-ring may also be damaged by chafing against a sharp edge on the backup ring where the ring is scarf cut, by chafing against the end of the backup ring helix or chafing against a sharp edge of the circumferential groove. Seal failures may also result from installing rings in improper sequence on the sleeve or by reason of installation of the O-ring or the backup ring facing in the incorrect direction.